This specification relates to data processing and content presentation.
The Internet enables access to a wide variety of resources. For example, video, audio, web pages directed to particular subject matter, news articles, images, and other resources are accessible over the Internet. The wide variety of resources that are accessible over the Internet has enabled opportunities for content distributors to provide content items with resources that are requested by users. Content items are units of content (e.g., individual files or a set of files) that are presented in/with resources (e.g., web pages), for example, in response to a content item request that is initiated by code included in, or associated with, the resource. An advertisement is an example of a content item that advertisers can provide for presentation with particular resources, such as web pages and search results pages.